/**
 * 背景图绘制
 *
 */
function Background() {
    // 图片地址数据
    this.imgArr = [Tool.getImage('./images/bg_01.jpg'), Tool.getImage('./images/bg_02.jpg'), Tool.getImage('./images/bg_03.jpg'), Tool.getImage('./images/bg_04.jpg'), Tool.getImage('./images/bg_05.jpg')];

    // 当前显示图片的索引
    this.index = 0;

    // 初始化
    this.init = function() {

    }

    this.init();

    // 绘制
    this.draw = function() {
        ctx.drawImage(this.imgArr[this.index], 0, 0);
    }
}